In Fahrenheit 451, one of Professor Faber's strongest character traits is his cowardice. Faber is very open about this trait, as he tells Montag when he visits his apartment:
"Mr Montag, you are looking at a coward."
Faber believes himself to be a coward because he witnessed first-hand the development of academic censorship and did nothing. He did not speak out, for example, nor did he encourage people to continue to read books. Once the fireman system was established, Faber "grunted a few times," but it was already too late to reverse this process.
This cowardice does have one redeeming feature, however. It leads Faber to create his own communication device which looks similar to the Seashell Radio. This device enables Faber to keep in touch with Montag when he meets with Captain Beatty and is in great need of emotional and intellectual support.